1. Field of the Invention
The present invention relates generally to aerosol generation. More specifically, the present invention relates to the use of mouthpiece entrainment airflow members for controlling aerosol size distributions from an aerosol generator.
2. Description of Related Art
Aerosols are useful in a wide variety of applications. For example, it is often desirable to treat respiratory ailments with, or deliver medicaments by means of, aerosol sprays of finely divided particles of liquid and/or solid, such as powders, liquid medicaments, and the like, which are inhaled into a patient""s lungs. Aerosols are also used for such purposes as providing desired scents to rooms, applying scents to the skin, and delivering paint and lubricant.
Various techniques are known for generating aerosols, particularly in the field of medicine. For example, U.S. Pat. Nos. 4,811,731 and 4,627,432 both disclose devices for administrating medicaments to patients in which a capsule is pierced by a pin to release medicament in powder form. The user inhales released medicament through an opening in the device. Medicaments in liquid form are known to be delivered by generation of an aerosol with a manually operated pump. The pump draws liquid from a reservoir and forces it through a small nozzle opening to form a fine spray.
Both of these methods of generating an aerosol for the delivery of medicaments suffer from problems. The aerosols produced by these techniques contain substantial quantities of particles or droplets which are too large to be inhaled. Persons who have difficulty in generating a sufficient flow of air through the device to properly inhale the medicaments, such as asthma or emphysema sufferers, have particular difficulty in using these devices.
An alternate means of delivering a medicament is generating an aerosol including liquid or powder particles by means of a compressed propellant, usually a chloro-fluoro-carbon (CFC) or hydrofluous alkane (HFA), which entrains the medicament, usually by the Venturi principle. Such inhalers are usually operated by depressing a button to release a short charge of the compressed propellant which contains the medicament through a spray nozzle, allowing the propellant encapsulated medicament to be inhaled by the user. However, it is difficult to properly synchronize the inhalation of the medicament with depression of the actuator. Further, large quantities of medicament or other materials are not suitably delivered by this method. This method is better suited to delivery of such materials as antiperspirants, deodorants and paints.
Many aerosol generators also are unable to generate aerosols having an average mass median aerosol diameter (MMAD) less than 2 to 4 microns, and are incapable of delivering high aerosol mass flow rates, such as above 1 milligram per second, with particles in the range of 0.2 to 2.0 microns. A high aerosol mass flow rate and small particle size are particularly desirable for better penetration of the lungs during medicament administration, such as for asthma treatment.
Large particles generated by metered dose inhalers may be deposited in the mouth and pharynx of the patient, rather than inhaled into the lungs. Further, what is inhaled may not penetrate the lungs deeply enough. Therefore, it is known to add a spacer chamber to a pressurized inhaler mechanism in order to allow the propellant time to evaporate, decreasing the mass median aerosol diameter of the particles. See, for example, U.S. Pat. No. 5,855,202 to Andrade and Eur. Respir. J. 1997; 10:1345-1348. Particles from metered dose inhalers may have an MMAD of 5-6 xcexcm. The use of a spacer chamber in such a case reduces the particle MMAD to about 1.5 xcexcm or greater, enhancing medicament deposition in the lung as opposed to the mouth or throat. See, for example, Eur. Respir. J. 1997, 10:1345-1348; International Journal of Pharmaceutics, 1 (1978) 205-212 and Am. Rev. Respir. Dis. 1981, 124:317-320.
Spacer chambers also are known to affect the output of the aerosol device because of the static charge which may be created therein. Medicament particles may be deposited in spacer chambers by electrostatic attraction to the spacer chamber wall, by inertial impaction, or by gravitational settling over time. Further, different medicaments behave differently within such spacer chambers based on particle size, particle charge, and the like. Thus, loss of medicament occurs within spacer chambers and is a drawback to effective spacer chamber use. See Eur. Respir. J. 1997; 10:1345-1348.
Therefore a need exists for a device which provides differing aerosol size distributions of an aerosol produced by an aerosol generator depending on the needs of a patient. Moreover, this device should allow adjustment of a aerosol size distribution of an aerosol produced by an aerosol generator.
The present invention fills the aforementioned needs by providing an aerosol generator having an airflow entrainment control member which allows for control of the aerosol size distribution of an aerosol exiting the aerosol generator. The airflow entrainment control member may be adapted for different aerosol size distributions depending on the needs of the user.
In one embodiment of the present invention, an aerosol generator includes a housing, a heater, a mouthpiece, a source of liquid material to be volatilized and an airflow entrainment control member. The housing includes a flow passage disposed therein which allows for heating of material from the source of material as the material passes into the flow passage. The heater is disposed along the flow passage and heats the flow passage, thereby volatilizing the material within the flow passage. The mouthpiece is located proximate an outlet end of the flow passage such that upon volatilization of the material within the heated passage, the volatilized material passes into the condensation region of the mouthpiece. The airflow entrainment control member is also disposed about the outlet end of the flow passage within the mouthpiece. The airflow entrainment control member is configured to control volume and/or velocity of air passing into the mouthpiece such that the air admixes with the volatilized material and forms an aerosol. Since the airflow entrainment control member controls volume and/or velocity of air passing into the mouthpiece, the airflow entrainment control member may be used to control the aerosol size distribution delivered by the aerosol generator.
In another embodiment of the present invention, a method for generating a volatilized material using the aerosol generator described above includes supplying liquid material to a flow passage contained within a housing of the aerosol generator, heating of the liquid material in the flow passage and directing the volatilized liquid material out of the flow passage and into the mouthpiece for admixing with external air passing through an airflow entrainment control member disposed proximate the outlet of the flow passage. The airflow entrainment control member is configured to control the volume and/or velocity of the external air passing into the mouthpiece, thereby controlling the aerosol size distribution of an aerosol delivered by the aerosol generator. In this embodiment, the airflow entrainment control member includes one or more airflow passages disposed therein. When the airflow entrainment control member is provided with a constant volumetric airflow rate, the size and number of the air passageways alters and controls the velocity of the available entrainment air in a condensation region of the aerosol generator. In this embodiment, the volumetric airflow rate of air into the airflow entrainment control member may also alter and control the velocity of the available entrainment air in the condensation region of the aerosol generator.
In a further embodiment of the present invention, a method for manufacturing the aerosol generator described above includes attaching the airflow entrainment control member to the aerosol generator housing at the downstream end of the flow passage.
In yet another embodiment of the present invention, an airflow entrainment control member in accordance with the present invention, may include a cone configuration disposed at a given angle. In this embodiment, a constant volumetric air flow rate is supplied to the cone where the angle of the cone determines the volume of entrainment air available. Therefore, the cone angle alters and controls the volume of entrainment air available in the condensation region. In this embodiment, the volumetric airflow rate of air supplied to the cone may also be altered. The ratio of available entrainment air in the condensation region will be controlled by the cone angle, thus controlling aerosol particle size.